Social networking giant Facebook's co-founder Mark Zuckerberg has been dropped from the list of the world's ten richest technology billionaires.

Zuckerberg's fortune dropped by over $420 million last week as Facebook shares fell to around $20 in New York, a record low.

According to the Bloomberg Billionaires Index, Zuckerberg is now worth $10.2 billion.

He is about $400 million behind James Goodnight, the co-founder of software maker SAS Institute, who now ranks as technology's 10th- richest person, The Sydney Morning Herald reports.

According to the paper, Zuckerberg's fortune is based on his ownership of 503.6 million shares of Facebook, including 60 million options that have an exercise price of six cents a share.

He also has about $150 million in cash and other liquid assets.